The present invention generally relates to the measurement of torque, and more particularly to a system and method for measuring torque using filtration of light to detect angular displacement of a pair of wheels.
In most mechanical applications, mechanical power is transferred in the form of torque. Typically, one end of an at least partially rigid shaft is rotated, causing the opposite end to rotate in turn, thereby transferring the mechanical power from one end of the shaft to the other end. Drive shafts are frequently substantially rigid, so that the two ends rotate at substantially the same time and angular speed. However, many drive shafts include a relatively flexible portion, which permits a substantially increased angular displacement between the ends of the drive shaft at a given torque. Such relatively flexible portions are often known as xe2x80x9ctorsion bars,xe2x80x9d and may be included, for example, in order to give a softer feel in applications where the driving torque is supplied by a human operator. One example of a common application is in the steering column of an automobile.
Torque-measuring devices are used in many applications to observe the torque being applied to a drive shaft. In particular, torque-measuring devices are used in many applications in automobiles. One reason it may be useful to measure torque is that such drive shafts may be prone to failure when exposed to excessive torque, or when exposed to moderate torque for extended periods. High-speed torque transmission can result in premature failure of a drive shaft caused by uncorrected flexing of one or more members of the drive train, for another example. Yet another reason it may be useful to observe the torque on a drive shaft is to ensure safe operation of the mechanism being driven. For example, if the torque on a drive shaft used to roll up a power window suddenly and greatly increases, it may be because someone or something has been caught between the window and the doorframe. A torque detector may therefore be used to interrupt the power to the drive shaft, to prevent injury to a person or damage to the window.
Torque-measuring devices typically measure an angular displacement, which is then related back to a torque through a calibration of the detector. Some methods for measuring displacement are strain gauges, magnetism, and optics. Once this displacement is measured, it is necessary to transmit a signal from the shaftxe2x80x94which may be rotating at a high angular velocityxe2x80x94to appropriate electronics for acquisition and processing. Some of the means of transmission are hardwiring (suitable only for stationary shafts), RF, magnetic, and optical. Whatever mechanism is used, it must typically be a separate system from that used to observe the angular displacement.
Such torque-measuring devices sometimes detect the angular displacement by using of a pair of wheels or similar apparati, affixed to coaxial drive shaft portions, which are permitted to angularly displace with respect to one another with torsion of the shaft. The wheels are more or less perpendicular to the axis of the drive shaft, and bear some means of encoding their positions relative to one another. Such encoding means sometimes include a magnetic field, optical reflectors, or other elements which must be separately constructed and affixed to the wheels. Therefore, systems employing such means are more expensive and less reliable. Also, the position of each wheel is often observed independently, and then the two positions are compared. Such systems require two position-detection mechanisms, and so are more expensive and less reliable than a system in which the position of one wheel relative to the other can be made with a single sensor.
Therefore there is a need for a system for detecting torque in a drive shaft that is inexpensive and reliable. The present invention is directed towards meeting that need, amongst others.
A system and method for measuring torque according to the present invention comprises a pair of drive shaft segments connected by a torsion bar, a wheel affixed to each of the drive shaft segments and having at least one slot cut through it, a light source positioned on the side of one of the wheels opposite the other, and a light detection device on the opposite side of the other wheel positioned to detect light from the light source which passes through the slots in both wheels. The slots are positioned in the wheels such that the pattern of light that can pass from the light source, through both wheels and to the detector, changes as the angular position of the wheels changes relative to one another. The light detection device observes the changes in this pattern of light to produce a signal indicative of the torque on the drive shaft that is producing the observed angular displacement of the wheels relative to one another.
A first embodiment system for detecting angular displacement in a shaft comprises: a first rotating member, having a first slit pattern therethrough, and being affixed to the shaft; a second rotating member, having a second slit pattern therethrough, and being affixed to the shaft; a light source positioned on a side of said first rotating member opposite said second rotating member; and a light detector positioned on a side of said second rotating member opposite said first rotating member such that light from said light source which would otherwise be incident on said light detector is substantially blocked by said first and second rotating members, except for light which passes through said first and second slit patterns. Said first and second slit patterns are adapted to create a pattern of light incident on said light detector that varies according to an angular position of said first rotating member relative to said second rotating member; and said light detector is adapted to produce a position signal responsive to a position of said pattern of light incident on said light detector.
A second embodiment system for detecting angular displacement between a first position and a second position on a shaft comprises: a first rotating member, having a first slit pattern therethrough and being affixed to said first position on the shaft, the first slit pattern consisting of a series of identical first slits regularly spaced about an axis of rotation of said shaft, and each of said first slits running both radially and angularly, relative to an origin of a set of radial coordinates located on an axis of rotation of the shaft; a second rotating member, identical to said first wheel and affixed to said second position on the shaft, but oriented to face in the opposite direction along said shaft relative to said first rotating member; a light source positioned on a side of said first rotating member opposite said second rotating member; and a position sensitive device positioned on a side of said second rotating member opposite said first rotating member such that light from said light source which would otherwise be incident on said light detector is substantially blocked by said first and second rotating members, except for light which passes through said first and second slit patterns. Said first and second slit patterns are adapted to create a pattern of light incident on said light detector that varies according to an angular position of said first rotating member relative to said second rotating member; and said light detector is adapted to produce a position signal responsive to a position of a centroid of said pattern of light incident on said light detector.
A third embodiment system for measuring the angular displacement between a first and second positions on a shaft comprises: a first rotating member, having a first slit pattern therethrough and being affixed to said first position on the shaft, the first slit pattern consisting of a series of identical first slits regularly spaced about an axis of rotation of said shaft, and each of said first slits running both radially and angularly, relative to an origin of a set of radial coordinates located on an axis of rotation of the shaft; a second rotating member, identical to said first wheel and affixed to said second position on the shaft, but oriented to face in the opposite direction along said shaft relative to said first rotating member; a light source positioned on a side of said first rotating member opposite said second rotating member; and a position sensitive device positioned on a side of said second rotating member opposite said first rotating member such that light from said light source which would otherwise be incident on said light detector is substantially blocked by said first and second rotating members, except for light which passes through said first and second slit patterns. Said first and second slit patterns are adapted to create a pattern of light incident on said light detector that varies according to an angular position of said first rotating member relative to said second rotating member; and said light detector is adapted to produce a position signal responsive to a position of a centroid of said pattern of light incident on said light detector. The system further comprises a circuit adapted to convert said position signal into a displacement signal corresponding to the angular displacement between said first and second rotating members that has been determined to produce a pattern of light having the position corresponding to said position signal.
A fourth embodiment system for measuring torque in a shaft comprises: a first rotating member, having a first slit pattern therethrough, the first slit pattern consisting of a series of identical first slits regularly spaced about an axis of rotation of said shaft, and each of said first slits running both radially and angularly, relative to an origin of a set of radial coordinates located on an axis of rotation of the shaft; a second rotating member, identical to said first wheel, but oriented to face in the opposite direction along said shaft relative to said first rotating member; a light source positioned on a side of said first rotating member opposite said second rotating member; a position sensitive device positioned on a side of said second rotating member opposite said first rotating member such that light from said light source which would otherwise be incident on said light detector is substantially blocked by said first and second rotating members, except for light which passes through said first and second slit patterns; and a circuit adapted to convert said position signal into a torque signal corresponding to the torque that has been determined to produce a pattern of light having the position corresponding to said position signal.
A first embodiment method of detecting angular displacement between a first position and a second position on a shaft comprises: providing a first rotating member affixed to the first position and a second rotating member affixed to the second position, each of the first and second rotating members having at least one slit therethrough; determining a relationship between angular displacement between the first and second positions and a pattern of light produced by filtration of substantially planar light through at least one slit in each of the first and second rotating members; and observing the pattern of light to determine the angular position of the first rotating member relative to the second rotating member.
A second embodiment method of detecting torque in a shaft comprises: providing a first rotating member and a second rotating member each having at least one slit therethrough; determining a relationship between a torque on the shaft and a pattern of light produced by filtration of substantially planar light through at least one slit in the first rotating member and at least one slit in the second rotating member; and observing the pattern of light to determine the angular position of the first rotating member relative to the second rotating member.
A third embodiment method of measuring torque in a shaft, comprises: providing a first rotating member and a second rotating member each having at least one slit therethrough; determining a relationship between a torque on the shaft and a pattern of light produced by filtration of substantially planar light through at least one slit in the first rotating member and at least one slit in the second rotating member; observing the pattern of light to determine the angular position of the first rotating member relative to the second rotating member; relating the angular position of the first rotating member relative to the second rotating member back to a torque on the shaft using the relationship. The observing the pattern of light is substantially limited to observing a radial position of the pattern of light relative to an axis of rotation of said first and second rotating members.